Evacuated tube water hammer pile driving

ABSTRACT

Driving long piles into submerged lands with a liquid ram or spear generated in an evacuated tube. Various drivers are enclosed. In one embodiment, the pile itself is used as at least a portion of the working chamber for generating water hammer.

United States Patent 1 m1 3,824,797 Wisotsky July 23, 1974 EVACUATEDTUBE WATER HAMMER [56] References Cited DRIVING UNITED STATES PATENTS 1lflvemorl Serge Wisnisky, Sharon, MaSS- 3,604,519 9/1971 Chelminski173/1 e 3,638,738 2/1972 Varnell 6l/53.5 [73] Assgnee' Mamn 3,646,5982/1972 Chelminski 61/535 [22] Filed: June 30, 1972 2 App]. No: 2 7 753Primary Examiner-Jacob Shapiro Attorney, Agent, or FirmRobert R. PriddyRelated US. Application Data [63] Continuation-impart at" Ser. No.l63,422, July [6,

I971, abandoned [57] ABSTRACT Driving long piles into submerged landswith a liquid Cl 5/5 ram or spear generated in an evacuated tube.Various 181/5 H drivers are enclosed. In one embodiment, the pile it-[Sl] Int. Cl E0211 7/10, GOlv 1/38 self is used as at least a portion ofthe working cham- [58] Field Of Search 6l/53.5, 63, 46.5, 173/]; her forgenerating water hammer 181/.5 H; ll4/206; 175/56 34 Claims, 14 DrawingFigures Wig IGI

"TENTH- 2 SHEEI 2 0f 5 WWW w wlllll EVACUATED TUBE WATER HAMMER PILEDRIVING CROSS-REFERENCE This is a continuation-in-part of an abandonedprior copending application Ser. No. l 3,422, tiled July l6, 1971, andnow abandoned, the disclosure of which is hereby incorporated byreference.

BACKGROUND The kinetic energy output of a pile driver is the product ofits driving mass and its velocity at the instant of impact with a pile.The emplacement of piles in the ground by pile driving is accomplishedby transmitting the kinetic energy of a hammer or other driving mass toa pile in sufficient quantity to cover nonproductive energy consumingfactors such as impact stresses, radiation, reflection and ground quake,and to overcome the friction, elasticity and inertial impedencecomponents of the pile and ground.

Increasingly larger land-based and offshore structures are constructedyear after year. Larger structures demand longer and more massive pilesfor their foundations, more deeply embedded in the ground. Thisrequirement is particularly severe in the case of large offshoreinstallations such as ship terminals, and oil drilling, production andstorage facilities. Without suitable foundations, such structuresweighing tens of thousands of tons can be readily dislodged and toppledby heavy storms, large vessels bumping, earthquakes, ice floes, oftenwith catastrophic loss of life, damage to the environment and loss ofinvested capital. Thus, to provide adequate load-bearing and to preventpull-out, req i t i q v n rflatwasirsslssfisst e several feet indiameter, weighing hundreds of tons, and for continuing the driving todepths of soil penetration where driving resistance is severe.

A complex series of relationships pertaining to pile and soiTcharacteristics, driving environ rnentfec onomics and materials governsthe design of a pile driver. However, generally speaking, the advent ofpiles of greater mass and conditions productive of more severe drivingresistance require drivers of increasing kinetic energy output. Intheabsence of adequate driving energy, that which is available isconsumed largely or completely by the aforementioned nonproductiveenergy consuming factors, leaving little or no energy to drive the pile.Under such conditions, some help is obtained by palliatives such asdrilling a pilot hole, water jetting or grouting into an over-size hole,but these measures normally reduce load-bearing capacity. Thus, as eachnew generation of more massive piles and more severe driving conditionsarises, drivers of greater energy output must be designed.

The kinetic energyqu tput of an existing hammer can be increased byincreasing either its mass or its impact velocity. The latteralternative is unattractive for a number of reasons.

First, there is the matter of the efficiency with which the hammertransfersenergy to the pile. In a complete inelastic collision between ahammer and pile, the kinetic energy remaining after impact forovercoming the nonproductive factors and driving the pile is inproportion to the ratio of the hammer mass divided by the total mass ofhammer plus pile. An increase in pile mass without a correspondingincrease in hammer mass results in a reduction of driving efficiency.

Also, higher hammer velocities are more predisposed to produce highlocal impact stresses. When the latter exceed the yield point of thepile material, kinetic energy is wasted and efficiency reduced.

For these and other reasons, manufacturers discourage the use of a piledriver in which the hammers mass is less than one-fourth that of thepile, and a mass ratio of one-half is generally recommended forland-based operations.

This presents a dilemma in off-shore pile driving. The largest steamhammer pile drivers currently in use in off-shore/marine work arelimited, practically, by safety considerations relative to theirhandling in stormy weather, to weights on the order of 60 tons (hammermass about 30 tons). Consequently, they usually are inadequate to drivethe larger piles due to massmismatch.

For instance, with a ZOO-ton pile, the energy transfer efficiency of a30-ton hammer would be percent X 30/(30 200) or about 13 percent.Moreover, even this relatively small amount of energy transferred to thepile is not altogether effective in driving for other reasons statedbelow.

The picture is further complicated by the fact that the energy in a pileis effective to penetrate the soil only if there is a proper impedancematch between the force-time-displacement characteristics of the driverand corresponding parametric thresholds of the soil. The availablealternatives for varying the force-timedisplacement characteristics of asteam hammer are limited, and this presents practical problems as thetip and sides of a pile often pass through strata of widely varyingcharacteristics as the pile penetrates the earth.

Thus, under the severest conditions, pile driving is an arduous, timeconsuming and expensive task which sometimes ends in failure to achievedesign loadbearing capacity or depth. Also, the inability to drive largepiles to sufficient depths often necessitates driving a larger number ofsmaller piles, so that as many as eight or 16 piles may be required forthe foundation of a single log of a multi-leg offshore structure.

Bearing in mind the storm-weather safety considerations mentioned above,it is of interest that at least one pile driver manufacturer hasproposed for offshore operations a pile driver, nominally rated atalmost 500,000 ft. lb., weighing on the order of 230 tons, equivalent tothe weight of several locomotives. Lifting this gigantic mass andadequately securing it during storm conditions present major challenges.Nevertheless, the fact that at least some of those active in the artseem ready to accept these formidable challenges suggests the severityof the problems and limitations with which the pile driving art is nowstruggling.

SUMMARY OF THE INVENTION The method of the present invention is carriedout in a long, massive pile which is, or is intended to be, part of thefoundation for a large offshore structure. The pile has its tip embeddedin the subsoil of a body of wa ter. An evacuatable enclosure withsidewalls and a lower barrier is effectively coupled with the tip of thepile for transmitting driving forces exerted upon said barrier to saidtip. The method comprises: evacuating at least a portion of saidenclosure, by removing water and at least a portion of any gases orvapors which may be present in the evacuated portion and evacuatingsufficiently to provide space for acceleration and deceleration of amass of water adequate to produce the necessary force and energy fordriving said pile; accelerating along the axis of said pile a mass ofwater which moves substantially independent of said pile; suddenlydecelerating said mass against said barrier, thereby convertinghydraulic kinetic energy to a water hammer driving pulse for drivingsaid pile into said sub-soil and repetitively evacuating, accelerating,decelerating and driving as aforesaid. Using this method, it is possibleto generate powerful mechanical impulses whose force-timecharacteristics can be tailored over a wide range of values to bettermatch the driving requirements of various pile and soil conditions.Other advantages will be discussed along with certain preferredembodiments of the invention as illustrated in the accompanying drawingsand text.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical elevation,foreshortened and partially broken out, showing an evacuated tube waterhammer driver in which the evacuatable enclosure is a tube other thanthe pile itself.

FIG. 2 is a schematic diagram of a driven similar to that shown in FIG.1, but provided with a pipe coupler and alignment means for securing thedriver within a pile.

FIG. 3 is a sectional view of a coupler for the FIG. 2 driver.

FIG. 4 is a schematic diagram in which the evacuateble enclosure isdefined at least in part by the walls of the pile, the motor-pumpcombination, water hammer valve and control means being similar to thatdescribed in FIG. 1.

FIGS. 5 and 6 are schematic diagrams of steam-reset water hammer piledrivers in which the evacuatable enclosure is defined at least in partby the walls of the pile.

FIGS. 7 through 9 are schematic diagrams of condensable vapor reset piledrivers in which the evacuatable enclosure is a tube separate from butcoupled to the pile, and in which various different kinds of condensablevapors are employed.

FIGS. 10 through 12 are schematic diagrams of means insertable in theevacuatable enclosures of the previously described water hammers forvarying the water hammer impulse.

FIGS. 13 and 14 are schematic diagrams of freepiston evacuatableenclosure water hammers in which the pistons are reset by mechanical andfluid pressure means respectively.

DESCRIPTION OF PREFERRED EMBODIMENTS In accordance with the invention,the enclosure walls can be at least partly or wholly, defined by a tubeseparate from the pile being driven, as disclosed by FIGS. 1-3, 7-9 and14 hereof. FIG. 1 represents a configuration of a pile l drivenunderwater into'the ground 100 by a top-mounted hammer. The pile l issecurely fastened to the hammer 3 by a coupling means 2. This coupling 2may take the form of simply bolted flanges or a more sophisticatedmechanical clamping arrangement similar to the scrollorpneumatically-operated machine tool lathe chucks which are well-knownand will not be described further. The pile hammer 3 in the present caseincludes hammer tube 4, made of flanged sections of heavy-walled tubingbolted together and contains a shock-mounted electric motor 5 hydraulicpump 6 combination near its bottom. (The motor pump positions may beinterchanged.) The pump 6 evacuates the water out of the hammer tube 4through a center-mounted pipe 7 discharging vertically out its top. Thepump 6 axially supports the discharge pipe 7 or, in otherconfigurations, vice versa. On the top-most section of the water hammertube 4 is mounted the fastopening water control valve 8 and itspneumatically operated actuator 9. When open, valve 8 freely admitswater from the surrounding body of water through the valve body and itsinlet 12 into hammer tube 4. A wire rope sling 10 supports the entireassembly from the surface and also conveys the power and control harnessIl thereto.

The design of the water control valve 8 may be such that rapid openingthereof is aided by the force generated by the ambient hydrostatic headacting on the valve. In order to prevent the inrushing water fromexerting any drag forces on the pump 6 and motor 5 assembly, the liquidlevel is controlled to prevent the draw-down of water to the pump level.The casings of the pump, motor and discharge pipe should be made strongenough to withstand the resulting water hammer pressure. When required,the motor-pump-discharge pipe assembly can be made free-floating andmechanically shock-isolated axially from the water hammer tube by alower compression spring (not shown) which supports the static airweight of the motor-pump-pipe assembly and an upper compression spring(not shown) which helps the gravity return of the pump assembly to itsnormal mid-position. A hydraulic type shock absorber (not shown) can beused to provide viscous damping to reduce oscillations. Further shockresistance can be provided by making the motor pump critical componentsneutrally buoyant in their respective liquid by means of low densityconstruction materials and high density liquids incorporated in theirrespective frames. Motor conductors and control cables pass from thesurface to the motor 5 and valve 8 through the water-tight power andcontrol harness 11.

When the pile is of sufficient length and diameter, and also tofacilitate the handling of long assemblies, the hammer tube 4 may belocated internally within the pile as shown in FIG. 2, using anyinternal coupling, such as that (40) shown in FIG. 3. This permitsincremental upward repositioning of the hammer as the pile l is driveninto the bottom 100. It also permits coupling of the driver to the pileat a position which is closer to the sub-soil than the top of the pile,giving an improved driving action. Concentricity alignment rings 42 maybe secured to each water hammer tube flange joint as shown in FIG. 2.

To secure the hammer within the pile high pressure i s .4. t9-tl 9ws oidt salca i y 522i the pile coupled 40 through port 54, FIG. 3. This flowcauses the cylinder frame 55 to move downward over the piston 56. Thepiston shaft is secured to the base 57 that is bolted to the bottomflange 48 of the water hammer tube 4. When the cylinder frame 55 movesdownward it creates a toggle action in the multiplicity of links 58. Theresultant mechanical advantage varies as the cotangent of the anglebetween the link and the ra dial normal. Consequently, hard-tooth shoes59 slide radially outward in T slot guides in the base 57 and bite intothe pile walls. Simultaneously, the fluid in the upper cylindricalcavity 60 is exhausted through port 61. A four-way electricallycontrolled valve (not shown) can be used to control the influx andefflux of the pressurized fluid, which may be hydraulic or air. Torelease the pile coupled, the influx and efflux ports on the piston baseare interchanged by control valve action. The compression spring 62 inthe upper cylinder 60 retracts the entire mechanism when the airpressure is off. This pile coupler also can be used in the enddriveconfiguration.

In accordance with the invention, the enclosure walls can be at leastpartly, or wholly, defined by the walls of the pile being driven, asdisclosed by FIGS. 4 through 6, and 13, hereof. FIG. 4 represents aconfiguration of a pile 1 driven underwater into the ground 100 with theaid of a module which includes parts similar to the pile driver of FIG.1, and which therefore bear like reference numerals.

Extending axially through the control valve 8 and actuator 9 is adischarge pipe 7 which communicates with and supports a pump 6 by thepump discharge outlet. The pump in turn supports an electric drive motor5. The valve 8, actuator 9, pipe 7, pump 6, motor 5, and cap 120 towhich they are secured constitute a unitary module which can be matedtemporarily, during driving, with each of a series of piles.

Cap 120 is in water-tight sealing engagement with the pile mouth 1 andmay be provided if desired, with means for remote-controlled release,e.g., a latch and trip-wire (not shown) to the surface, for releasingthe module from the pile when driving has been completed. A wire ropesling 10 is provided for lowering and lifting the module onto and off ofthe piles, and also conveys the power and control cable harness 11thereto. The module is serviced by a barge 124 having a winch 125 andcable 126 for lifting and lowering the module and a drum 127 for payingout and winding up the power and control cable harness 11.

When the module is mated to a pile, the pile performs the function ofthe hammer tube of the FIG. 1 embodiment, and the operation is the same.In this case, the evacuatable enclosure is defined by the cylindricalwalls of the pile 1 and the inner surface 121 of the pile tip 122. Theenclosure is coupled with the tip through the wall material of the pile.

During the operation of the device, water is evacuated from that portionof the enclosure which is at or above the level of pump inlet 123 anddischarged through the discharge pipe 7. Upon opening of the fast actingvalve 8, water is drawn through valve inlet 12 and is acceleratedinwardly along the axis of the pile by the ambient hydrostatic head.Because the valve is provided with a large opening, the mass of watermoving along the axis of the pile substantially fills the crosssectionof the evacuated portion of the enclosure. The water is unrestrained andtherefore continues moving substantially independent of the pile untilit is suddenly decelerated against the barrier provided by the innersurface 121 of the pile tip. the water being substantially at itstheoretical bulk modulus when decelerated. In this connection, it shouldbe noted that the mass of water can be decelerated against the barriereither directly or per se (if provision were made for completelyemptying the pile before admitting the water) or indirectly, such as bycontacting the water accumulated in the lower portion of the pile. As aresult of such deceleration at the water's theoretical bulk modulus, thehydraulic kinetic energy is converted to a powerful water hammer drivingpulse for driving the pile into the sub-soil.

The pile hammer 3 can be freely modified, as desired. For instance, themotor 5 and/or pump 6 may be located outside hammer tube 4 or pile Iprovided the pump inlet is in communication with the interior of thetube at a position spaced along the tube axis from water control valve8. Hammers can be employed which have water control valves at both endsand controls which would permit driving along the tube axis in eitherdirection. Configurations may be fabricated for horizontal driving.

Different kinds of valves also may be used. Such others includespring-loaded, hydraulically and electromagnetically actuated linear androtary shear varieties; metal, plastic and elastomeric pinch-off forms,free jet and fluidic submerged jet and pressure-switched groups; and,change-of-state valving techniques. Specific models are identified asspool and gridiron, sliding and rotary shear valves; conventional globe,gate, plug, ball, balanced/eccentric-pivoted poppet and butterfly, andflapper valves; resilient sleeve hydraulically, pneumatically, andmechanically squeezed pinch valves; jet pipes; electroviscous andmagnetoviscous forms.

Any other design of evacuatable water-hammer driver may be used in thepresent invention. Included are those in which evacuation of the wateris accomplished by condensable vapors or gas injected into or generatedwithin the chamber. In such cases, a water control valve is notessential to start the flow of liquid in the hammer tube. These areillustrated in FIGS. 5-9, which also show that the enclosure walls mayor may not be at least partly defined by the walls of the pile itself.

IN FIG. 5, a barge 124 is anchored above the pile I, having a tip 122embedded in the subsoil and an upper end which is submerged and in opencommunication with the ambient sea water surrounding it. On the barge isa steam generator 105, control valve 127 for metering steam flow throughthe insulated steam hose 11, a winch 125, and a cable 126. The steamhose extends downwardly to the pile, along with cable 126, which by anappropriate sling 13] supports and retrieves an insulated rigid steampipe 132 prepositioned inside the pile by surface-released latchingspiders 133. The latching mechanism (not shown), and spiders must bestrong enough to withstand the bottom of the steam pipe 132 terminatesin a steam check valve 134 fitted with steam nozzle 135 open downward.Thus, when the valve 127 opens for a predetermined interval to emit aburst of high pressure steam (which of necessity must be ofsubstantially higher pressure than the hydrostatic head) an expandingsteam bubble is produced which forces upwardly that water which ispresent in the pipe above the level of the steam nozzle 135.

Preferably, the volume of the steam burst is regulated to just evacuatethe pile l of water. The steam is preferably of superheat quality andreleased in sufficient quantity to just evacuate the pile 1 of water.The efflux upward momentum generates a corresponding down thrust. Italso causes a sudden vapor condensation when the tube pressure is drivennegative The attendant evacuation by change of the physical state of thesteam results in reversing the water flow to generate the downdrivingwater hammer impulse to the pile l. [f a non-condensable gas like airwere used to the exclusion of steam, a spring-like compliance would beimparted to the water, severely reducing the power of the hammer blow. AHelmholtz type of damped oscillation is then generated, whose frequencydepends on the volume of entrapped air, hydrostatic head, and mass ofwater in the tube.

FIG. 6 represents a similar arrangement which operates in the samemanner. However, in this case, the pile I has an open-ended tip 136, andthe barrier 140 is a remote-controlled incrementally-moved gripperassembly (similar in construction and operation to FIGS. 3 and 2,respectively). Said assembly secures check valve 134 terminating steampipe 132 feeding steam nozzle 135 (of folded horn construction) whichexhausts upwards. As the pile is driven downward the water which isentrapped in cavity 143 between the barrier 140 and soil plug 144exhausts out through drain pipe 142. The gas-filled compliant balloonI41, precharged to ambient pressure, absorbs the momentary volumetricincrements of the water displaced during driving. The hydraulictightness of the water barrier 140 is not critical when leakage absorbedby the compliance 141 subtracts only an insignificant amount from thetotal dynamicpressure.

FIG. 7 discloses a condensable vapor reset driver in which theevacuatable tube is defined by a tube 4 other than the pile l itself.The tube 4 is coupled, to the pile, for instance, by a coupler (notshown) similar to that in FIG. 3. The controls for the coupler, thesteam generator 10S and control valve 104 may be mounted on a surfacebarge (not shown) and may pass to the pile in any desired manner, suchas for instance as disclosed in FIG. 5. In the operation of thisembodiment, the steam control valve 104 is open momentarily to meter theproper amount of steam from generator 105 to the interior of the pile.The operation is the same as the FIG. 5 embodiment.

FIG. 8 represents an arrangement similar to FIG. 7, utilizing atwo-phase combustible mixture consisting of a pressurized fuel such ashydrogen, or a hydrocarbon as kerosene or alcohol, in container 106, afuelmetering valve 107, a pressurized oxidizer such as oxygen incontainer 108, and its corresponding metering valve 109. The fuelcombustion chamber 110 is located within the water hammer tube 4. Thecomponent 111 represents either the external ignition source, such as aspark plug, or proprietary catalyst for the monopropellent type rocketfuels such as hydrogen peroxide or hydrazine. For hypergolic(spontaneous combustion upon mixing) type propellants the igniter 111may be eliminated. On the other hand, liquid (water)borne particles ofsolid type propellants or explosives may be metered via the valve 107,caught in the screened combustion chamber, and fired off by means of theigniter Ill. The products of combustion are used to expel the water aspreviously discussed. These combustion products will be condensable, orat least partly so, due to their water vapor content.

Similarly, FIG. 9 also represents the use of socalled rocket fuelswherein the combustion chamber 110 is external to the water hammer tube4. The combustion products metering valve 112 controls the waterevacuation cycle and also acts as a check valve against the water hammerpressure. The remaining parts are similar to those shown in FIG. 8.

Practically, the principal limitation on the generation of larger valuesof water hammer within a single pipe may be the circumferential tensileor hoop stress. As will be shown, the generation of water hammer at a1,000 ft. depth in a 2-foot diameter steel pipe requires a wallthickness of 2.34 inches in order to keep the stress down to 69,000 psiWhile this is not an excessive working stress for modern alloy steels,it still exceeds structural grade ratings. Since the invention isnormally used in limited access or restricted environments, a low safetyfactor can be employed. To avoid the use of excessively massive pipewalls, reinforcement in the form of filament winding or an axial seriesof external or internal spaced reinforcing rings is recommended. Thedistributed spring mass configuration of the latter also reduces thetransonic velocity of wave propagation along the pipe. Two advantagesfollow, namely, reduction of hoop stress and increase of impulseduration. The use of pipe wall materials with a lower elastic moduluslike aluminum or resinated fiberglass achieves a reduction in waterhammer pressure by lowering the transonic velocity. For these to befully effective under water, additional acoustic pressure releasematerial like cork may be applied at the ambient water interface inorder to preclude acoustic loading. Another method of reducing wallstresses, by slowing down the axial velocity, is to use a series oftruncated cone baffles and 151 as illustrated in FIG. 10 or to spiralthe water in the tube by uni-directionally twisted or alternatelytwisted bundles of smaller diameter tubes or baffles. Thus, the waterhammer tube 4 of any of the preceding embodiments may be provided with aplurality of twisted tubes 152 within the tube 4 and extending axiallyof at least a portion of the tube which defines the evacuatableenclosure. Where the tube 4 includes a discharge pipe 7 or otherequipment along its axis, the spiral tubes 152 may be arranged around orabove them. Similarly, baffles 155 and 156 of varying rotation may beused, as disclosed in FIG. 12. The longer travel path provided by thesevarious means proportionally creates a longer pulse.

Where the water hammer device is provided with a valve to start thewater flow, the water hammer intensity can be reduced by retarding therate at which the valve goes from full closed to full open position.

Thus, for a given driving application (assuming a given depth, pile massand soil conditions) it is possible to tailor the force-timecharacteristics of the water hammer impulses by a suitable selection ofthe length and diameters of th water hammer tube, and the reinforcementand material of construction thereof. Also, one may employ the acousticpressure release material, baffles and valve opening rate as discussedabove. Thus, it will be seen that the method has far more flexibilitythan is provided by the conventional steam hammer.

When the water hammer tube is provided with a unidirectional helix, acomponent of mechanical torque and rotation can be generated by thechecked angular momentum of the falling mass of water. This can increasethe penetrating power of the pile driver in certain soils. The screw"vs. the nail" action also improves a friction pile's load bearingcapacity, especially when the lead" or helix angle is optimized for thesoil conditions.

FIG. 13 discloses one example of that class of evacuatable tube waterhammer drivers which include one or more free pistons. in the presentcontext, a free piston is one which, during at least a portion of itsmovement between the extreme limits of its travel, is not directlycoupled to or is at least substantially independent of, the pile.Configurations are possible in which the free piston, provided withmeans to raise it in the evacuatable chamber, can replace the pumpmotorcombination. in the preferred mode of operation, the piston will replaceboth the pump-motor combination and the water control valve.

In FIG. 13 a barge 134 is anchored over a pile I having its tip 122embedded in sub-soil 100. The piles open mouth 130 is submerged. From awinch 125 on the barge descends a cable 126 through pile mouth 130 to apiston 160. The latter fits closely enough within the pile walls to atleast partially and preferably substantially completely bar the entry ofwater into the space below the piston as it is raised, the need for ordesireability of packing 161 being determined in part by the speed atwhich the piston is to be raised and lowered.

Operation of this embodiment simply involves repetitively andalternately raising the piston 160 with winch 125 and dropping thepiston, which may, if desired come to rest against a cushion block 163.Raising of the piston evacuates an enclosure defined by the pile tip andside walls. Quick release of the piston and rapid descent thereofthrough the pile accelerates a mass of water above the piston. This massis suddenly decelerated by indirect contact through the rigid pistonwith the barrier provided by th cushion block 163 when the pistonstrikes the latter. This, in turn, generates the water hammer impulsewhich drives the pile.

To minimize drag and inertia forces which would retard the fall ofpiston 160, a clutch may be used to disengage the winch reel from itsdrive motor during the fall of the piston. For large piston loads amulti-sheaved block and tackle, mounted on the top of the hammer tube,may be employed. The main hook made in the form of a bull gear may bedisengaged from the piston by rotation, pivoting around a bushed holdingpin. The required mechanical power may be provided by a small electricor hydraulic motor-driven pinion. A small rope which follows the pistondown its stoke may act as a guide for reengaging the lifting hook. Otherquick make-break configurations are the commerically available wirelineovershot latching clips for removing downhole core barrels from diamondbits left inside petroleum wells.

A guided long rack and motor-driven pinion means may also be used toraise the piston. A high pressureangle stubby gear tooth profilefacilitates the easy disengagement of the pinion from the rack by aguickacting cam or hydraulic piston means. The rack can ride down withthe piston and the pinion assembly remain fixed at the top of the hammertube.

Similarly, another piston-raising means may employ a split nut fastenedto hydraulically or cam-actuated chuck jaws to engage and quicklydisengage a long, threaded screw fastened to the piston. The nut isrotated by a motor driven pinion meshing with a bull gear made integralwith the chuck, all mounted in top of the water hammer tube.

Another method would use a hydraulically-actuated cylinder to lift thepiston. A hydraulic chuck. on the end of the cylinder rod, latches anddisengages the piston.

For shorter and faster piston hammer strokes a tubemounted electric orhydraulic motor-driven cam is used to provide a relatively slow lift andfree drop to the piston.

instead of packing or piston rings, a rolling diaphragm type seal may beused to keep the water out of the interior of the water hammer tube. Asuitablyshaped fillet at the bottom of the stroke supports theelastomeric-impregnated fabric against the highamplitude water hammerpressure pulse.

in the above-described embodiments, the water hammer tube has beenentirely submerged in the water in which it is operating, the preferredmode of carrying out the invention. This makes use of the hydrostatichead available in the water to power the driving impulse. Also, thesubmerged-operation feature of the invention offers the possibility ofeasier handling during storm conditions. However, in other cases,especially shallow water applications, the water hammer tube may be atleast partially above the surface of the water. Whether the evacuatableenclosure is defined by a tube separate from the pile, or by the pileitself, the water for generating the water hammer pulses may be providedby an upward extension of the pile or the tube, which is filled withwater, or by a reservoir located above the hammer tube as shown in FIG.14.

IN FIG. 14 is shown a pile 1 partially embedded in sub-soil and havingits upper end protruding above the waters surface. A driver 17! isreleasably secured in the top of the pile by a coupler 40 similar tothat disclosed in FIG. 3, like parts of the respective couplers beingidentified in the drawings by the same reference numerals. To the base57 of the coupler is secured the base 172 of the driver.

Extending upwardly from the base 172 is an upright, elongated waterhammer tube 4. A reservoir 188 is supported by the tube 4 and connectedthereto by flared walls 189 to promote smooth flow of water 190 betweenthe tubes and reservoir. The reservoir may be pressurized if desired byforcing in gas or vapor through inlet 192. A central column 173 issuitably secured to the base 172 and extends upwardly and coaxially withthe water hammer tube 4 and thence at least part way into reservoir 188,where it maybe supported by a three-legged spider 191 secured to thereservoir walls, only one leg of which is shown in the drawing.

Piston 174 is mounted for vertical or axial reciprocation on column 173between base 172 and stop secured toward the upper end of the column.Both the piston and base 172 are reinforced to withstand the mechanicalshock associated with water hammer pressures. The piston itself may ofcourse contribute some driving momentum during operation, but normally,during driving, the mass of the piston is less, and usuallysubstantially less than half, the mass of the fluid (water) which isabove it or which enters the tube 4 during the down stroke.

The piston has a central aperture 177 of slightly greater diameter thanthe outside of column 173, and has an outer diameter slightly less thanthat of the inner diameter of the water hammer tube 4. Suitable sealsmay be provided if desired in the clearances between the piston on theone hand and the pile and column on the other. However, when operatingwith a small pressure differential across the piston. e.g., l atmosphereor less, leakage of water and steam past the piston will be minimal.Thus, it is possible to fabricate the apparatus in a way which providesa close but essentially dragfree relationship between the piston and theother parts. Also, making the piston neutrally buoyant relative to watermay reduce the pressure differential and discourage leakage.

Connected to a suitable steam supply (not shown) is a steam conduit 178with control valve 123. Conduit 178 feeds passages in base 172terminating in steam outlets 179. When the control valve 123 is openedto emit a burst of steam from the outlets 179 at a pressure greater thanthe ambient water pressure above piston 174, it will be forced upwardlyin tube 4. When the piston retains sufficient upward momentum aftercontrol valve 123 closes, the resultant further expansion of the spacebeneath the piston can super-cool the steam and condense it, thusevacuating the space beneath the piston. Where, because of insufficientmomentum or other reasons, there is not sufficient auto-cooling of thesteam, cool water may be sprayed into the space beneath the piston bywater conduits and spray nozzles (not shown) fitted into the centralcolumn and/or base, or into the side walls of tube 4.

In order to keep the evacuatable enclosure free of steam condensate, andpossibly of cooling water where such is used, the base 172 may be fittedwith a drain pipe 182 and valve 181. Valve 181, like steam valve 123,will normally be opened during the raising of piston 174 and closed onthe down stroke.

In certain apparatus, e. g., that having a cam-actuated free piston, itmay be found desirable to adjust the actuation of the valve to maintainthe hydraulic pulse repetition rate at an operational resonance of thesystem. This can be accomplished by placing sensors on the driver and/orpile and/or ground and automatically actuating the valve in response tosignals from the sensors.

Although water is used as an example, the working fluid is notnecessarily limited thereto. In a closed system. any liquid may be used.

EXAMPLE When working with water hammer tubes of about 50 feet andlonger, one can obtain driving pulses which are approximately two ormore times as long as with the large steam hammer described in thecomparison example, Longer pulses are obtained with a hammer tube of 100feet in length. This may be illustrated with a water hammer tube of 24inch diameter schedule 160 (2.343 inch wall) steel pipe 100 feet longand weighing 54,209 pounds. Ancillary equipment includes a pump toevacuate the tube at some convenient rate. a watertight cap at one endof the tube, and a fast acting valve at the other end.

After the pipe is evacuated and the control valve is suddenly opened,the water entrance velocity U,,.,," at the 1,000 ft. depth "In" isUitioo JZgh {2 X 32.2 ft./sec( 1.000 34)ft.]

259 ft./sec.

v c 4890 ft./sec.

L22 3.3 X 10' psi. X 19.3 in. J1 ET 1 29 X 10 p.s.i. X 2.34 in.

= 4670 ft.lsec.

The water hammer pressure is p pv U 1.99 slugs/ft X 4,679 ft/sec X 259ft/sec 16,700 psi.

The corresponding simple tensile hoop stress in the pipe walls is s=pD/2t (16,700 psi X 19.3 in)/(2 X 2.34 in) 69,000 psi.

The water hammer impulse force is F p S, 16,700 psi X 293 in. 4,900,000lbs.

The time duration of the impulse force on the capped end is T 2L/v (2 Xft.)/4,670 ft/sec 0.0428 sec.

The hydraulic momentum of the incoming water, just before impact, is

(MU) pS LU 1.99 slugs/ft X 2.03 ft X 100 ft X 259 ft/sec 104,500slug-ft./sec 104,500 lb-sec.

The hydraulic kinetic energy of the incoming water is KE A: X 13,000lbs/32.2 ft/sec X (259 ft/sec) 13.5 X 10 ft.1bs. 18.3 Mega Joules Theincoming hydraulic power is W rr/Bp D U =1r/8 X 1.99 slugslft. X (1.61ft) X (259 ft/sec) 35 X 10 ft.lbs./sec 47.5 Megawatts As a check, thework required to evacuate the pipe against the ambient hydrostatic head,or the potential energy of its cavity is PE ambient pressure X pipevolume p g h S, L 64 lbs/ft x 1,034 ft x 203.5 re 13.5 x 10 ft.lbs.

The water hammer power is W rr/Sp D U v 1r/8 (1.99 slugs/ft) (1.61 ft)(259 ft/sec) (4,670 ft/sec) 631 X l0ft.lbs./scc. 855 MegawattsCOMPARISON An example of the contemporary state-of-the art is referencedfor comparison. One of the largest, commercial single-acting steam/airhammers for land-based or offshore piledriving is the 060 size rated at180,000 ft.lbs. The practical underwater operational limit is 200 ft.The striking energy, obtained by a 60,000 lb: weight free-dropping 3ft., is 1/ 7 th of the water hammer value from the two foot pipeexample. At the theoretical terminal velocity of U V g7i= X tsec X ft13.9 ft/sec, its momentum, (MUM, 60,000 lbs/32.2 ft/sec X 13.9 ft/sec25,900 lb.sec. or onefourth of that acquired by the water hammerexample. The principal feature of the water hammer, however, is in therelatively long time duration of the impulse force. In order to improveon this desirable characteristic, the steel piledriving hammer uses anexpendable wooden or resinated-fabric cushion block insert between theram and the pile to diminish the impact shock. Wave propagation theory,using computerized solutions of finite difference equations, has beenapplied to a math model describing system behavior of What happens when(the) hammer hits (the) pile," Eng. News Record, 5 Sept. 1957, Edw. A.Smith; also, refer to E.A.L. Smith, Pile-Driving Analysis by the WaveEquation," J. Soil Mechanics and Foundations Div., Proc. ASME, Aug.1960. A further investigation, correlating piledriving characteristicswith its load bearing capacity, (Forehand and Reese, Pile-DrivingAnalysis Using the Wave Equation," Princeton Univ., M.S. EngineeringThesis, 1963), discloses that the impulse duration, defined as the timethe velocity remains positive," is of the order of 10 milliseconds forthe steel hammer blow or one-fourth of that in the water hammer example.If so, then the 30 ton steel hammer impulse force is F, 25,900lb.sec./0.0l sec 2,600,000 lbs.

or roughly one-half of the water force. The mechanical power transferrate of the steel hammer is, roughly, W, [80,000 ft. lbs/0.01 sec. 24.4M W, or 1/35 of the water hammer power. If the impulse duration of thesteel hammer blow is shorter, the force obviously increases in inverseproportion, but then a new difficulty arises in establishingcompression, and displacement, simultaneously along the entire length ofa long pipe. For example, in a steel pile 200 ft. long, even with anundamped (unclamped) sound velocity of 16,600 ft/sec. in steel, it takes12 milliseconds for the impulse to reach the tip. With concrete piles,this trouble is further aggravated because sound velocity in concrete isone-third slower. Some contemporary offshore foundation designs call forloads up to 2,000 tons from piles 200-600 ft. long, 3-8 ft. in dia.,weighing 100-200 tons, in up to 1,000 ft. of water. Withoutsupplementary techniques involving pre-drilling or jetting such pilesare practically undrivable by the steam-air hammer even when spliced toextend to the surface.

From the foregoing, it may be seen that the invention provides manyadvantages. It makes feasible a large increase in driving capability.And this can be done using a smaller mass ratio (driving mass versuspile) than has heretofore been thought advisable in steam hammeroperations. That is, larger impulses can be generated using a drivingmass which is less than one-fourth that of the pile. This, in turn,makes it possible to drive piles without the use of palliatives such aspilot hole drilling, water jetting and grouting into an oversized hole,which measures can reduce pile load-bearing capacity.

The pressure-time characteristics of the water hammer impulse can betailored over a wide range of values to match corresponding requirementsof the pile and soil. Thus, driving impedance can be better matched tothat of the earth than when operating with for instance a steel hammer.

Under the longer impulses which can be generated by a water ram or spearhaving a length to diameter ratio of 10 or more, long piles, e.g., L/D15, move more nearly as a unit, e.g., their driving action is more likethat of a nail, rather than a worm, in which one part moves ahead whileother parts are held back. Thus, a greater fraction of the drivingenergy is usefully expended in overcoming displacement skin friction, toadvance the pile, rather than being tied up in the rubber-like groundquake. With the long pulses which may be provided with water hammer ifdesired, unwanted standing wave conditions in the pile can be preventedmore effectively. The invention renders unnecessary the use of a cushionblock, as sometimes required with a steel hammer, thereby eliminatingthe inelastic collision energy loss associated therewith.

Certain important advantages are associated with the convenient mannerin which the invention may be applied under water. With the driversubmerged, it may be handled with greater safety and ease during stormconditions. Coupling of the driver to the pile at a point below its topend helps to reduce losses of driving energy attributable to themechanical compliance of the pile. Submerged operation provides inherentcapacity for generating larger pulses as submergence increases, andparticularly a depths greater than 200 feet where hydrostatic backpressure aggravates the venting problem of the air operated hammer,where thermal line losses preclude the steam driven hammer and whereconventional vibratory driving requires such a relatively largeback-mass for preload and such low frequencies that reaction forcesnecessary for driving become ineffective without excessively largeexcursions. Handling is facilitated because the driving mass can bedrained from the apparatus when it is being transported and lifted abovethe surface.

Moreover, water hammer operation makes it convenient to twist the pileas it is driven downward, such as by including helical baffles in thewater hammer tube which impart a twisting motion thereto. In some cases,especially where the lead" or helix angle is optimized for the soilconditions, this can improve the piles load bearing capacity.

In view of the foregoing, it is apparent that the present invention is abroad one, and that many changes may be made in the foregoingembodiments without departing from the spirit of the invention.

What is claimed is:

1. 1n the driving of piles underwater, wherein the pile has its tipembedded in the subsoil of a body of water and an evacuatable enclosurewith side walls and a lower barrier is effectively coupled with the tipof the pile for transmitting driving forces exerted upon said barrier tosaid tip, the method which comprises: evacuating at least a portion ofsaid enclosure, by removing water and at least a portion of any gases orany vapors which may be present in the evacuated portion and evacuatingsufficiently to provide space for acceleration and deceleration of amass of water adequate to produce the necessary force and energy fordriving said pile; accelerating along the axis of said pile a mass ofwater which moves substantially independent of said pile in saidevacuated portion of said enclosure; suddenly decelerating said massagainst said barrier, thereby converting hydraulic kinetic energy to awater hammer driving pulse for driving said pile into said subsoil; andrepetitively evacuating, accelerating, decelerating and driving asaforesaid.

2. A method in accordance with claim 1 wherein said evacuatableenclosure is beneath the surface of said body of water, and the mass ofwater accelerated along the axis of said pile is accelerated under theinfluence of the hydrostatic head in said body of water.

3. A method in accordance with claim 1 wherein said evacuatableenclosure is in communication with a reservoir, and the mass of wateraccelerated along the axis of said pile is accelerated under theinfluence of a hydrostatic head in said reservoir.

4. A method in accordance with claim 3 wherein said reservoir ispressurized with gas or vapor.

5. A method in accordance with claim 1 wherein said enclosure is withinsaid pile.

6. A method in accordance with claim 1 wherein the walls of saidenclosure are defined at least in part by the walls of said pile.

7. A method in accordance with claim 1 wherein the driving force isapplied to said pile through a coupling which is below the top of thepile.

8. A method in accordance with claim 7 wherein the coupling is closer tothe subsoil of said body of water than to the top of said pile.

9. A method in accordance with claim 1 wherein the enclosure isevacuated by pumping.

10. A method in accordance with claim I wherein said enclosure isevacuated with a condensable vapor.

11. A method in accordance with claim 10 wherein said condensable vaporis condensed, and the acceleration of said mass of water is commenced,by spraying cool water into the condensable vapor.

12. A method in accordance with claim 1 wherein said enclosure isevacuated with combustion gases that are at least partially condensable.

13. A method in accordance with claim 1 wherein said enclosure isevacuated by forcing the water away from the barrier with piston means.

14. A method in accordance with claim 13 wherein said piston means ismoved by pressure exerted thereon by condensable vapor, and saidcondensable vapor is then condensed to commence the acceleration of saidmass of water along the axis of said pile. I

15. A method in accordance with claim 1 wherein the acceleration of saidmass of water along the axis of said pile is commenced by the rapidopening of valve means communicating between said enclosure and a sourceof water under pressure.

16. A method in accordance with claim 15 wherein said valve is retainedclosed during evacuation of said enclosure and opens in response to thewater reaching a predetermined level in the evacuation of saidenclosure.

17. A method in accordance with claim 15 wherein a hydrostatic head insaid source of water is applied to said valve for assisting in the rapidopening thereof.

18. A method in accordance with claim 15 wherein the water hammerintensity is controlled by controlling the rate at which said valve isopened.

19. A method in accordance with claim 1 wherein said pile is driven ineither direction by valves at both ends of said enclosure and bycontrols for driving along the tube axis in either direction.

20. A method in accordance with claim 1 including selectively retardingthe axial velocity of said mass of water for varying the pressure andtime characteristics of the water hammer driving pulse to compensate forvarying strata and driving conditions.

21. A method in accordance with claim 20 wherein said axial velocity isretarded by retarding the opening of a valve which commences theacceleration of said mass of water.

22. A method in accordance with claim 20 wherein said axial velocity isretarded by baffle means in said enclosure.

23. A method in accordance with claim 20 wherein said axial velocity isretarded by imparting a twisting motion to the mass of water which movesalong the axis of said enclosure.

24. A method in accordance with claim 1 wherein the mass of wateraccelerating along the axis of said enclosure substantially fills thecross section of said enclosure.

25. A method in accordance with claim 1 wherein the water deceleratedagainst said barrier has substantially theoretical bulk density onimpact.

26. A method in accordance with claim 1 wherein the mass of waterdecelerated against said barrier has less than one-fourth the mass ofsaid pile.

27. A method in accordance with claim 1 wherein said pile has a lengthto diameter ratio of equal to or greater than 15, said pile is submergedin water 200 feet deep or deeper, said evacuatable enclosure is beneaththe surface of said body of water, and the mass of water acceleratedalong the axis of said pile is accelerated under the influence of thehydrostatic head in said body of water.

28. In the dirving of piles underwater, wherein a pile having a lengthto diameter ratio of equal to or greater than l5 has its tip embedded inthe subsoil of a body of water 200 feet deep or deeper and anevacuatable enclosure with side walls and a lower barrier is effectively coupled with the tip of the pile for transmitting driving forcesexerted upon said barrier to said tip, the method which comprises:evacuating at least a portion of said enclosure, by removing water andat least a portion of any gases or any vapors which may be present inthe evacuated portion and evacuating sufficiently to provide space foracceleration and deceleration of a mass of water adequate to produce thenecessary force and energy for driving said pile; accelerating along theaxis of said pile a mass of water which moves substantially independentof said pile in said evacuated portion of said enclosure; selectivelyretarding the axial velocity of said water mass for varying the pressureand time characteristics of a water hammer driving pulse to be generatedby impact of said mass against said barrier; suddenly decelerating saidmass against said barrier, thereby converting hydraulic kinetic energyto said water hammer driving pulse for driving said pile into saidsubsoil; and repetitively evacuating, accelerating, decelerating anddriving as aforesaid.

29. A method in accordance with claim 28 wherein said axial velocity isretarded by retarding the opening of a valve which commences theacceleration of said mass of water.

30. A method in accordance with claim 28 wherein said axial velocity isretarded by baffle means in said enclosure.

31. A method in accordance with claim 28 wherein said axial velocity isretarded by imparting a twisting motion to the mass of water which movesalong the access of said enclosure.

32. In the driving of piles underwater, wherein a pile having a lengthto diameter ratio of greater than or equal to IS, a diameter of threefeet or larger and a length of 200 feet or longer has its tip embeddedin the subsoil of, and is completely submerged in, a body of water atleast about 200 feet deep, and has an evacuatable enclosure beneath thesurface of said body of water with side walls and a lower barriereffectively coupled with the tip of the pile for transmitting drivingforces exerted upon said barrier to said tip, the method whichcomprises: evacuating at least a portion of said enclosure, by removingwater and at least a portion of any gases or any vapors which may bepresent in the evacuated portion and evacuating sufficiently to providespace for acceleration and deceleration of a mass of water adequate toproduce the necessary force and energy for driving said pile;accelerating along the axis of said pile under the influence of thehydrostatic head in said body of water a water ram or spear having alength to diameter ratio of or more which moves substantiallyindependent of said pile in said evacuated portion of said enclosure;suddenly decelerating said mass against said barrier, said water beingat substantially theoretical bulk density on impact, thereby convertinghydraulic kinetic energy to a water hammer driving pulse for drivingsaid pile into said subsoil; and repetitively evacuating, accelerating,decelerating and driving as aforesaid.

33. A method in accordance with claim 32 in which the evacuated portionof said enclosure is 50 feet in length or longer.

34. in the driving of piles underwater, wherein the pile has its tipembedded in a subsoil of a body of water and an evacuatable enclosurewith side walls and a lower barrier is effectively coupled with the tipof the pile for transmitting driving forces exerted upon said barrier tosaid tip, the method which comprises: evacuating at least a portion ofsaid enclosure, by removing liquid and at least a portion of any gasesor any vapors which may be present in the evacuated portion andevacuating sufficiently to provide space for acceleration anddeceleration of a mass of the liquid adequate to produce the necessaryforce and energy for driving said pile; accelerating along the axis ofsaid pile a mass of said liquid which moves substantially independentlyof said pile in said evacuated portion of said enclosure; suddenlydecelerating said mass against said barrier, thereby convertinghydraulic kinetic energy to a liquid hammer driving pulse for drivingsaid pile into said subsoil; and repetitively evacuating, accelerating,decelerating and driving as aforesaid.

fgggg" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION pag3,824,797 Dated vember 5, 1974 Invent-(5) Serge S Wisotsky It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

b) lines 12 and 13, delete "the product" and insert a function and c)line 52, change the after "hole" to d) Column 2, line 44, delete "log"and insert leg.

e) Column 3, line 26, delete "driven" and insert -driver-.

f) Column 4, line 57, after "pile" insert and g) line 59, delete"coupled" and insert --coupler--.

h) Column 5, line 7, delete "coupled" and insert --coupler-'--.

i) Column 6, line 51, after "the" insert water impact forces,

and yet not unduly impede its flow. The

j) Column 7, line 18, after "downward" insert k) Column 8, line 41,delete "varying" and insert alternating 1) Column 9, line 46, delete"stoke" and insert stroke n) line 55, delete "g'uick-" and insert quick-:233? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO, 0Dated November 5,

Inventoz-(s) serge iSOtsky It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

n) line 58, delete "main" and insert mains-.

0) Column 11, line 51, delete and insert p) line 53, delete "160" inbold face type and insert 160-- in normal face type; and

q) lines 62 to 65, delete i000 2 9 [2 x 32. 2 ft/sec 1, 000 34 ft 259ft./sec.

and insert F2. 2 ft./sec (1, 000 34) 1%.]

259 ft./sec/ r) Column 12, line 48, delete "U and insert U s) Column 14,line 9, after"L/D" insert and t) I line 32, delete "a" and insert at u)Column 16, line 39, delete "dirving" and insert driving-.

v) Column 17, lines 6 and 7, delete "access" and insert J mg?" UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION November 5, 1974- PatentNo. 3:824v797 Dated lnventofl Serge S. Wisotsky W ars in theabove-identified pg g It is certified that error a hereby corrected asshown below:

and that said Letters Patent are axis .1

Signed and sealed this 11th day of March 1975'.

(SEAL) Attest:

' C. MARSHALL DANN Commissioner of Patents RUTH C. MASON A'ttestipgOfficer and Trademarks

1. In the driving of piles underwater, wherein the pile has its tipembedded in the subsoil of a body of water and an evacuatable enclosurewith side walls and a lower barrier is effectively coupled with the tipof the pile for transmitting driving forces exerted upon said barrier tosaid tip, the method which comprises: evacuating at least a portion ofsaid enclosure, thereby removing water and at least a portion of anygases or any vapors which may be present in the evacuated portion andevacuating sufficiently to provide space for acceleration anddeceleration of a mass of wAter adequate to produce the necessary forceand energy for driving said pile; accelerating along the axis of saidpile a mass of water which moves substantially independent of said pilein said evacuated portion of said enclosure; suddenly decelerating saidmass against said barrier, thereby converting hydraulic kinetic energyto a water hammer driving pulse for driving said pile into said subsoil;and repetitively evacuating, accelerating, decelerating and driving asaforesaid.
 2. A method in accordance with claim 1 wherein saidevacuatable enclosure is beneath the surface of said body of water, andthe mass of water accelerated along the axis of said pile is acceleratedunder the influence of the hydrostatic head in said body of water.
 3. Amethod in accordance with claim 1 wherein said evacuatable enclosure isin communication with a reservoir, and the mass of water acceleratedalong the axis of said pile is accelerated under the influence of ahydrostatic head in said reservoir.
 4. A method in accordance with claim3 wherein said reservoir is pressurized with gas or vapor.
 5. A methodin accordance with claim 1 wherein said enclosure is within said pile.6. A method in accordance with claim 1 wherein the walls of saidenclosure are defined at least in part by the walls of said pile.
 7. Amethod in accordance with claim 1 wherein the driving force is appliedto said pile through a coupling which is below the top of the pile.
 8. Amethod in accordance with claim 7 wherein the coupling is closer to thesubsoil of said body of water than to the top of said pile.
 9. A methodin accordance with claim 1 wherein the enclosure is evacuated bypumping.
 10. A method in accordance with claim 1 wherein said enclosureis evacuated with a condensable vapor.
 11. A method in accordance withclaim 10 wherein said condensable vapor is condensed, and theacceleration of said mass of water is commenced, by spraying cool waterinto the condensable vapor.
 12. A method in accordance with claim 1wherein said enclosure is evacuated with combustion gases that are atleast partially condensable.
 13. A method in accordance with claim 1wherein said enclosure is evacuated by forcing the water away from thebarrier with piston means.
 14. A method in accordance with claim 13wherein said piston means is moved by pressure exerted thereon bycondensable vapor, and said condensable vapor is then condensed tocommence the acceleration of said mass of water along the axis of saidpile.
 15. A method in accordance with claim 1 wherein the accelerationof said mass of water along the axis of said pile is commenced by therapid opening of valve means communicating between said enclosure and asource of water under pressure.
 16. A method in accordance with claim 15wherein said valve is retained closed during evacuation of saidenclosure and opens in response to the water reaching a predeterminedlevel in the evacuation of said enclosure.
 17. A method in accordancewith claim 15 wherein a hydrostatic head in said source of water isapplied to said valve for assisting in the rapid opening thereof.
 18. Amethod in accordance with claim 15 wherein the water hammer intensity iscontrolled by controlling the rate at which said valve is opened.
 19. Amethod in accordance with claim 1 wherein said pile is driven in eitherdirection by valves at both ends of said enclosure and by controls fordriving along the tube axis in either direction.
 20. A method inaccordance with claim 1 including selectively retarding the axialvelocity of said mass of water for varying the pressure and timecharacteristics of the water hammer driving pulse to compensate forvarying strata and driving conditions.
 21. A method in accordance withclaim 20 wherein said axial velocity is retarded by retarding theopening of a valve which commences the acceleration of said mass ofwater.
 22. A method in accordance with claim 20 wherein said axialvelocity is retarded by baffle means iN said enclosure.
 23. A method inaccordance with claim 20 wherein said axial velocity is retarded byimparting a twisting motion to the mass of water which moves along theaxis of said enclosure.
 24. A method in accordance with claim 1 whereinthe mass of water accelerating along the axis of said enclosuresubstantially fills the cross section of said enclosure.
 25. A method inaccordance with claim 1 wherein the water decelerated against saidbarrier has substantially theoretical bulk density on impact.
 26. Amethod in accordance with claim 1 wherein the mass of water deceleratedagainst said barrier has less than one-fourth the mass of said pile. 27.A method in accordance with claim 1 wherein said pile has a length todiameter ratio of equal to or greater than 15, said pile is submerged inwater 200 feet deep or deeper, said evacuatable enclosure is beneath thesurface of said body of water, and the mass of water accelerated alongthe axis of said pile is accelerated under the influence of thehydrostatic head in said body of water.
 28. In the dirving of pilesunderwater, wherein a pile having a length to diameter ratio of equal toor greater than 15 has its tip embedded in the subsoil of a body ofwater 200 feet deep or deeper and an evacuatable enclosure with sidewalls and a lower barrier is effectively coupled with the tip of thepile for transmitting driving forces exerted upon said barrier to saidtip, the method which comprises: evacuating at least a portion of saidenclosure, by removing water and at least a portion of any gases or anyvapors which may be present in the evacuated portion and evacuatingsufficiently to provide space for acceleration and deceleration of amass of water adequate to produce the necessary force and energy fordriving said pile; accelerating along the axis of said pile a mass ofwater which moves substantially independent of said pile in saidevacuated portion of said enclosure; selectively retarding the axialvelocity of said water mass for varying the pressure and timecharacteristics of a water hammer driving pulse to be generated byimpact of said mass against said barrier; suddenly decelerating saidmass against said barrier, thereby converting hydraulic kinetic energyto said water hammer driving pulse for driving said pile into saidsubsoil; and repetitively evacuating, accelerating, decelerating anddriving as aforesaid.
 29. A method in accordance with claim 28 whereinsaid axial velocity is retarded by retarding the opening of a valvewhich commences the acceleration of said mass of water.
 30. A method inaccordance with claim 28 wherein said axial velocity is retarded bybaffle means in said enclosure.
 31. A method in accordance with claim 28wherein said axial velocity is retarded by imparting a twisting motionto the mass of water which moves along the access of said enclosure. 32.In the driving of piles underwater, wherein a pile having a length todiameter ratio of greater than or equal to 15, a diameter of three feetor larger and a length of 200 feet or longer has its tip embedded in thesubsoil of, and is completely submerged in, a body of water at leastabout 200 feet deep, and has an evacuatable enclosure beneath thesurface of said body of water with side walls and a lower barriereffectively coupled with the tip of the pile for transmitting drivingforces exerted upon said barrier to said tip, the method whichcomprises: evacuating at least a portion of said enclosure, by removingwater and at least a portion of any gases or any vapors which may bepresent in the evacuated portion and evacuating sufficiently to providespace for acceleration and deceleration of a mass of water adequate toproduce the necessary force and energy for driving said pile;accelerating along the axis of said pile under the influence of thehydrostatic head in said body of water a water ram or spear having alength to diameter ratio of 10 or more which moves subStantiallyindependent of said pile in said evacuated portion of said enclosure;suddenly decelerating said mass against said barrier, said water beingat substantially theoretical bulk density on impact, thereby convertinghydraulic kinetic energy to a water hammer driving pulse for drivingsaid pile into said subsoil; and repetitively evacuating, accelerating,decelerating and driving as aforesaid.
 33. A method in accordance withclaim 32 in which the evacuated portion of said enclosure is 50 feet inlength or longer.
 34. In the driving of piles underwater, wherein thepile has its tip embedded in a subsoil of a body of water and anevacuatable enclosure with side walls and a lower barrier is effectivelycoupled with the tip of the pile for transmitting driving forces exertedupon said barrier to said tip, the method which comprises: evacuating atleast a portion of said enclosure, by removing liquid and at least aportion of any gases or any vapors which may be present in the evacuatedportion and evacuating sufficiently to provide space for accelerationand deceleration of a mass of the liquid adequate to produce thenecessary force and energy for driving said pile; accelerating along theaxis of said pile a mass of said liquid which moves substantiallyindependently of said pile in said evacuated portion of said enclosure;suddenly decelerating said mass against said barrier, thereby convertinghydraulic kinetic energy to a liquid hammer driving pulse for drivingsaid pile into said subsoil; and repetitively evacuating, accelerating,decelerating and driving as aforesaid.